The field of the invention is in the hermetic electrical feedthrough art.
Electrical feed-through connectors for hermetically sealed containers normally incorporate a ceramic insulator and Kovar metal for the connector pin and housing. Kovar is a well known, commerically available nickel-cobalt-iron alloy which has a low coefficient of expansion which is compatible with the coefficient of expansion of certain glasses and ceramic materials. Because of this compatibility, Kovar is commonly used to make hermetic seals. If Kovar connectors are used in lightweight aluminum housings, a problem is created by the incompatibility of the Kovar and aluminum. These two materials cannot be readily joined by welding or brazing. With a suitable plating, the two materials can be soldered, but due to the great difference in coefficient of expansion, high thermal stresses are induced during moderate temperature changes which exceed the capability of common solders. Consideration has also been given to the use of a soft metal gasket or seal ring between a flange on the Kovar seal and the aluminum housing, but with temperature changes there is relative motion at the seal, and with sufficient cycles the relative mechanical motion causes a leak to be created. The Kovar ceramic feed-through can be sealed to an aluminum housing with elastomeric seals, but even with the best type of rubber, such as Butyl, gases can permeate through the elastomeric seal at a rate which may not be acceptable for long-term applications.
The best known prior art is that described by the following patents: U.S. Pat. No. 2,459,193 to patentees Sparks et al; U.S. Pat. No. 3,189,677 to patentees Anthony et al; U.S. Pat. No. 3,637,917 to patentee Oates; and U.S. Pat. No. 3,865,970 to patentee Vrijssen.